A halftone image (multi-level image) having intermediate gradation is formed by performing multi-gradation recording with changing the dot ratio of each pixel. To form the halftone image by changing the number of dot data items, dither methods are widely used. Of various dither methods, the halftone type that forms dots is commonly utilized.
A dither method that forms a line-based image is known. In this method, a plurality of dots are formed for one pixel data and combined, forming a dot set extending diagonal to the recording direction, and the density is increased, thereby forming more dots. (Refer to, for example, Patent Document 1)
A color image processing device is known. (Refer to, for example, Patent Document 2) In this device, multi-level writing is performed for each dot by supplying electric current selectively to a plurality of heating elements of the thermal head, changing the diameter of resin-based ink dots and transferring the ink dots to the paper, and a multi-color image is thereby recorded.